Liquid level gauge

ABSTRACT

A combination visual liquid level warning gauge and filler plug for liquid filled tanks such as medium voltage switchgear and distribution equipment, having a cylindrical body of transparent material forming the plug which passes through the wall of the tank. The inner end of the cylinder is bevelled into two internally reflecting facets, which reflect a legend from both sides of a generally planar symbol-bearing area which bisects the angle between the facets within the transparent body. The refractive index of the transparent plug is selected to be close enough to that of the liquid in the tank that contact of the liquid with the facets will eliminate the internal reflection from the facets and render the legend invisible from the outer end of the plug. A socket is provided in the wall of the tank to receive the plug, and an expanded head on the plug seats against a collar on the socket to limit the plug movement into the tank. Mating apertures through the plug and collar permit insertion of a retaining pin, which then may be sealed against tampering by a lead seal.

D United States Patent 1 1 [111 3,796,098 Trayer Mar. 12, 1974 LIQUIDLEVEL GAUGE [57] ABSTRACT 7 Inventor; Frank Tray", 25 9 LaLanne Acombination visual liquid level warning gauge and CL, Los Altos Hills, Clif 94022 filler plug' for liquid filled tanks such as medium voltageswitchgear and distribution equipment, having a [22] F'led: 1972cylindrical body of transparent material forming the [2}] APPL 245,373plug which passes throughthe wall of the tank The inner end of thecylinder is bevelled into two internally reflecting facets, whichreflect a legend from [52] US. Cl. 715/327, 350/96 R, 350/252 both Sidesof a generally planar symbohbearing area [51] Int. Cl. Golf 23/02 whichbisects the angle between the facets i i the [58] Field of Search73/327; 1 16/1 18 R; transparent body. The refractive index f thetranSPar, 350/96 286; 340/244 380; ent plug is selected to be closeenough to that of the 85/ 5 CF liquid in the tank that contact of theliquid with the facets will eliminate the internal reflection from the[56] References Cimd facets and render the legend invisible from theouter UNITED STATES PATENTS end of the plug. A socket is provided in thewall of the 2,943,530 7/1960 Nagel 350/113 tank to receive the Plug, andan eXPanded head on the 2,430,616 11/1947 Pearson 350/112 X plug seatsagainst a collar on the socket to limit the 2,949,777 8/1960 Ferron 350/1 13 plug movement into the tank. Mating apertures l,6l7,932 2/1927 Worket al 350/113 through the plug and collar permit inse flgn of arel,883,97l l0/l932 Kryzanowsky 73/327 mining pin i h then may be sealedagainst tampep 3,273,267 9/1966 wlllman 73/327 X ing by lead seal.

470,507 3/1892 Risser 85/5 CP Primary ExaminerDonald O. Woodie!Assistant ExaminerDaniel M. Yasich Attorney, Agent, or Firm-Schapp andHatch 5 Claims, 7 Drawing Figures LIQUID LEVEL GAUGE BACKGROUND OF THEINVENTION This invention relates to a LIQUID LEVEL GAUGE, and moreparticularly to a device for giving visual warning of a liquid level inan enclosed tank.

Many enclosed devices depend for their proper functioning on themaintenance of a particular liquid level within the enclosure, and manysystems have been developed for gauging such liquid levels. Among suchsystems, however, few are well adapted for ultra-reliable performance inextremes of weather or for use on hazardous equipment such as mediumvoltage electrical switch gear and distribution equipment.

Prior art devices have often been too complex for the degree ofreliability required, or too expensive for practical application. Othershave been susceptible to fouling by the liquid, such as transformer oil,being gauged. Many, too, have been difficult to read or ambiguous intheir indication. Ideally, such a gauge should not require anindependent power source for its operation, and should not interferewith the integrity of the weatherproofing or submersibility of thedevice to which it is applied.

SUMMARY OF THE INVENTION The liquid level gauge of the present inventionhas no electrical or mechanically active parts, and is sufficientlysimple in construction to yield an extremely high reliability. Itssimple and self-contained nature and its use of ambient light forillumination render it quite resistant to fouling by the liquid beingmeasured, and permit its use in high hazard applications with safety.

The straightforward nature of the gauge also allows it to be applied tosubmersible and fully weatherproof enclosures without creating problemsin the submersibility. The overall safety of the system protected by thegauge is enhanced by the static nature of the gauge, since it is notdependent upon any power supply or mechanical apparatus for itsoperation, and since the gauge indication is so directly dependent uponthe physical presence or absence of the gauged liquid.

Accordingly, it is a principal object of the present invention toprovide a liquid level warning device of the character described whichwill visually indicate the absence of a desired liquid level within anenclosed tank.

It is a further principal object of the present invention to provide aliquid level warning device of the character described having a veryhigh degree of reliability and independence of environmental factors.

Another object of the present invention is to provide a liquid levelwarning device of the character described which provides a direct,unambiguous indication of low liquid level without susceptibility tofouling by the liquid, mechanical failure or power supply interruption.

A further object of the present invention is to provide a liquid levelwarning device of the character described which is simple andinexpensive in its construction, and

which will further serve as a'tamper-proof fill and in- BRIEFDESCRIPTION OF THE DRAWING The preferred forms of the present inventionare illustrated in the accompanying drawing, forming part of thisspecification, in which FIG. 1 is a perspective view of the liquid levelwarning device of the present invention, with portions thereof shown incross-section and portions of the tank to which it is attached shownbroken away for clarity, with the liquid level low;

FIG. 2 is a perspective view corresponding to that of FIG. 1, shown witha higher liquid level in the tank;

FIG. 3 is a cross-sectional view on an enlarged scale takenapproximately along the plane of lines 3-3 of FIG. 7, showing however amodified form of the head portion of the device;

FIG. 4 is a fragmentary cross-sectional view taken approximately alongthe plane of lines 4-4 of FIG. 3;

FIG. 5 is a fragmentary cross-sectional view taken approximately alongthe plane of lines 5-5 of FIG. 3;

' FIG. 6 is a fragmentary cross-sectional view corresponding to thelower portion of FIG. 3, shown with the liquid in the tank at a higherlevel, as in FIG. 2; and

FIG. 7 is a top plan view taken approximately along the plane of lines77 of FIG. 3. v

While only the preferred forms of the invention have been shown here, itshould be understood that various changes or modifications may be madewithin the scope of the claims attached hereto without departingfrom'the spirit of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings indetail, it may be seen that the liquid level gauge 11 of the presentinvention includes a body of transparent material 12 disposable throughthe wall 13 of a tank containing the liquid to be gauged and a receivingsocket 14 for the transparent body or plug 12. The socket I4 ismountable in the wall 13 of the tank and so dimensioned as to permit aportion of the body 12 to extend into a region of the tank occupied bythe liquid contents of the tank when it is filled to the desired level,while permitting a portion of the body 12 to be seen from outside thetank.

The body or plug 12 has an axis 16 generally corresponding to the normalline of sight from the exterior to the interior of the tank through thesocket 14, and a portion of the body 12 within the tank is faceted at anangle to the axis 16. As shown in the present embodiment, the facetedportion of the body 12 is the innermost end 17 of the body 12, with afacet shown at 18. The body 12 bears a legend area 19 therein adjacentthe facet 18 and visible from the outer end 21, of the bodyby reflectionof light from the facet 18 to the legend area 19 when the facet 1 8 isfree from contact with the liquid within the tank.

As may be seen from FIGS. 2 and 6, the legend area 19 is renderedinvisible when the facet 18 is contacted by the liquid within the tank,as the liquid impedes the necessary internal reflection from the facetto the legend and back by lowering the difference in refractive indicesencountered at the facet boundary to the point at which an incident rayparallel to the axis 16 is refracted rather than reflected at the facet.Although the present-device is operative if only one facet is formed onthe inner end 17 of the plug 12, it has been found advantageous to formtwo facets opposite each other,

and to place a two-sided legend, such as that shown in FIGS. 4 and 5,between the facets.

The most advantageous angle between the facet 18 and the axis 16 hasbeen found to be 45, especially when the legend area 19 is, as shownhere, generally the legend without reflection from a facet, and increasethe complexity of the device as well.

A pair of facets 18 are shown here, with the facets generallyperpendicular to each other and the legend borne on two sides of anopaque body of material 22 lying between the facets 18 adjacent theinner end of the transparent body 12. This configuration allowsreflection of different messages from each side of the body 22, as shownin FIGS. 4 and 5. The legend shown in those figures is, of course, onlyone of many possible warnings. Note the reversal side for side requiredof the FIG. legend and the top to bottom reversal required of the FIG.4.

The opaque body 22 may be formed of a piece of multi-layered plastic ofthe type known as Lamicoid, having at least twolayers of contrastingcolor, so that engraving of it will produce lettering of one color on abackground of another color. In the present application, one desirablecombination would be white letters on a red background, red for dangerand white for maximum legibility. The rectangular piece of plasticbearing the legend engraved on it may conveniently be ccmented into aslot 23 cut in the inner end of the transparent body 12. In such aprotected location, the liquid being gauged cannot foul or obscure thereadability of the legend. With the legend area in the configurationshown here, edge on to the viewing axis 16, the warning color of thebackground of the legend is essentially not visible to aviewer lookinginto the outer end of the body l2, when no reflection is taking placefrom the facet 18. Once reflection takes place, however, both thewritten legend and the warning color become visible to the viewer, withthe reflection operating to reorient the image of the legend-bearingopaque body 22 to a normal-reading direction.

The socket 14 is formed as a generally cylindrical tube passing throughthe wall 13 of the tank. A pair of apertures 24 are formed transverselythrough the outer end of the socket l4, and a matching, generallychordal aperture 26 is formed in the generally cylindrical body of theplug 12 so that the apertures 24 and 26 may be aligned when thetransparent plug body I2 is fully inserted into the socket 14. Aretaining pin 27 of a generally D-shaped configuration may have thestraight leg of the pin inserted through the apertures 24 and 26 to holdthe plug 12 in place against internal tank pressure or externaltampering. For additional security against tampering, the curved andstraight legs of the pin 27 may be brought together and fastened by alead seal 28.

As here shown, the plug 12 is sealed to the socket 14 by O-ring seals 29of oil-resistant material such as Neoprene, borne in circumferentialgrooves on the plug body 12 to maintain the submersible integrity of thetank and its contents. The use of O-ring seals allows the scaling to beindependent of the judgment of the operator inserting the plug 12, sincethe seating force is dependent only on the spacing between the plug 12and the'inner surface of the socket 14. It should be appreciated,however, that the gauge of the present invention could be constructedwith mating screw threads on the plug body 12 and the socket 14, with agasket provided between the head 31 of the plug and the outer end 32 ofthe socket, to complete the seal. Such an arrangement might well bedesirable in applications having high internal pressures in the tank,where the added pressure integrity would offset the advantage ofindependence of operator judgment shown in the O-ring seal arrangement.

The outer end 21 of the plug body 12 is formed into a head portion 31 ofenlarged diameter, which seats against theouter end 32 of the socket 14to limit the inward motion of the plug 12 in the socket 14. In the formof the invention shown in FIGS. 1 and 2, the top surface of the enlargedhead portion is generally flat. In the form shown in FIGS. 3 and 7, alens is formed by providing a curved top surface 33. The lens allowsviewing from off-axis positions, and magnifies the image of the legendarea 19. The preferred material for the transparent plug body 12 isLucite.

From the foregoing, it may be seen that a selfcontained liquid levelwarning device has been provided which will directly and unambiguouslyvisually indicate the absenceof a desired liquid level in a tank with ahigh degree of reliability and independence of the environment. Thedevice resists fouling by the measured liquid and is unaffected bymechanical or power failure, and is simple and inexpensive in itsconstruction. 1

I claim:

1. A liquid-level gauge for tanks and the like, comprising a body oftransparent material disposable through a wall of the tank, and

a receiving socket for said body, retainingly mountable in a wall of thetank and dimensioned to permit a portion of said body to extend into aregion occupied by the liquid contents of the tank when the tank isfilled to the desired level, and to permit a portion of said body to beseen from outside the tank,

said body having an axis generally corresponding to the normal line ofsight from the exterior to the interior of the tank through said socket,a tip portion of said body within the tank having two facetssymetrically arranged at an angle of approximately 45 to said axis, anopaque legend bearing area vertically mounted in said tip portion withopposite sides of the legend area each bearing separate and distinctletters or symbols oriented differently thereon, said letters or symbolsof a color contrasting that of said legend area, said legend area beingvisible from the outer end of said body by reflection from said facetsto said legend area of light rays passing generally parallel to saidaxis when said facets are free from contact with liquid within saidtank, whereby said legend area will be rendered invisible when saidfacets are contacted by liquid contents of said tank to impede lightreflection therefrom.

2. A liquid level gauge as described in claim 1, and wherein said twofacets are approximately perpendicular to each other.

3. A liquid level gauge as described in claim 2, and wherein said legendarea is borne on two sides of said opaque body of material locatedadjacent the inner end of said transparent body and between said twofacets, whereby said legend will be readable in normal orientation alongsaid axis after reflection of one side of said opaque body by each ofsaid facets when said facets are free of contact with liquid contents ofthe tank.

4. A liquid level gauge as described in claim 1, and wherein said gaugefurther comprises a retaining pin insertable through mating apertures insaid body and said socket to retain said body in said socket withoutobstructing the view of said legend from the exterior of the tank.

5. A liquid level gauge as described in claim 1, and

wherein said gauge further comprises at least one 0- ring seal betweensaid transparent body and said socket, and a retaining pin, said socketbeing formed as a cylindrical tube passing through the wall of the tank,said transparent body being formed as a cylindrical body fitting withinsaid cylindrical tube and sealed therebetween by said O-ring seal, saidtransparent body having an enlarged head portion adapted to seat againstthe outer end of said socket to limit inward motion of said transparentbody in said socket, said outer end of said socket having two transverseapertures therethrough along a chord of said cylindrical socket, saidtransparent body having a chordal aperture therethrough mating with saidapertures in said socket, said apertures being dimensioned to permitpassage of said retaining pin therethrough without obstructing the viewof said legend from the exterior of the tank.

1. A liquid-level gauge for tanks and the like, comprising a body oftransparent material disposable through a wall of the tank, and areceiving socket for said body, retainingly mountable in a wall of thetank and dimensioned to permit a portion of said body to extend into aregion occupied by the liquid contents of the tank when the tank isfilled to the desired level, and to permit a portion of said body to beseen from outside the tank, said body having an axis generallycorresponding to the normal line of sight from the exterior to theinterior of the tank through said socket, a tip portion of said bodywithin the tank having two facets symetrically arranged at an angle ofapproximately 45* to said axis, an opaque legend bearing area verticallymounted in said tip portion with opposite sides of the legend area eachbearing separate and distinct letters or symbols oriented differentlythereon, said letters or symbols of a color contrasting that of saidlegend area, said legend area being visible from the outer end of saidbody by reflection from said facets to said legend area of light rayspassing generally parallel to said axis when said facets are free fromcontact with liquid within said tank, whereby said legend area will berendered invisible when said facets are contacted by liquid contents ofsaid tank to impede light reflection therefrom.
 2. A liquid level gaugeas described in claim 1, and wherein said two facets are approximatelyperpendicular to each other.
 3. A liquid level gauge as described inclaim 2, and wherein said legend area is borne on two sides of saidopaque body of material located adjacent the inner end of saidtransparent body and between said two facets, whereby said legend willbe readable in normal orientation along said axis after reflection ofone side of said opaque body by each of said facets when said facets arefree of contact with liquid contents of the tank.
 4. A liquid levelgauge as described in claim 1, and wherein said gauge further comprisesa retaining pin insertable through mating apertures in said body andsaid socket to retain said body in said socket without obstructing theview of said legend from the exterior of the tank.
 5. A liquid levelgauge as described in claim 1, and wherein said gauge further comprisesat least one O-ring seal between said trAnsparent body and said socket,and a retaining pin, said socket being formed as a cylindrical tubepassing through the wall of the tank, said transparent body being formedas a cylindrical body fitting within said cylindrical tube and sealedtherebetween by said O-ring seal, said transparent body having anenlarged head portion adapted to seat against the outer end of saidsocket to limit inward motion of said transparent body in said socket,said outer end of said socket having two transverse aperturestherethrough along a chord of said cylindrical socket, said transparentbody having a chordal aperture therethrough mating with said aperturesin said socket, said apertures being dimensioned to permit passage ofsaid retaining pin therethrough without obstructing the view of saidlegend from the exterior of the tank.